A corpectomy is a surgical procedure wherein a portion of the vertebral body and adjacent intervertebral discs are removed to relieve pressure or decompress the spinal cord and nerves. A corpectomy cage is used to fill the space created by the vertebrae removal. Two types of cages are generally available: A solid fixed height cage and an expandable cage. Fixed cages are manufactured in various heights so that one cage can be selected to best fit the cavity created by the removed vertebral body. Alternatively, an expandable cage having a variable height can be used to maintain spacing of the vertebrae above and below the removed body material. Such expandable cages typically include telescoping members with a physical mechanism to retain the members at the selected height. For example, telescoping members are formed with threaded or ratcheting interconnections, or the use of pins, set screws and the like, to fix the members at a selected height.
Both types of cages have limitations and problems. Fixed or solid cages have excellent structural integrity, but are cumbersome to place. The fixed cage must be exactly the right height. Otherwise, if the cage is too big, it can cause over distraction to the vertebral bodies or damage the vertebral body above and below the cage. If the cage is too small, it can move out of position. Expandable cages are much easier to place and size correctly. However, the mechanical mechanism used to expand the cage may fail in vivo, which can lead to catastrophic results. The telescoping members are weight bearing so as to support the axial loads on the cage when the cage is implanted. Thus, the strength of the case depends upon the inner connection between the telescoping members. If the physiologic load becomes too great, the cage will collapse, thereby causing potentially serious medical problems for the patient. Thus, the structural integrity of an expandable case is less than a fixed or solid cage.
Some commercially available expandable cage are made of metal. These metal cages cause artifact on MRI or CT scans, thereby decreasing the ability to visualize nearby anatomy. Metal cages are also much harder than bone, and can telescope into the vertebral bodies above and below the cage. Commercially available fixed cages are made of other materials, such as carbon fiber, or plastic, which eliminate artifacts on MRI and CT scans.
Accordingly, a primary objective of the present invention is the provision of an improved expandable corpectomy cage which overcomes the problems of the prior art.
Another objective of the present invention is the provision of an expandable corpectomy cage having structural integrity and which is easy to use.
Still another objective of the present invention is the provision of an expandable corpectomy cage which is made of non-metallic materials so as to avoid scanning and imaging artifacts.
Yet another objective of the present invention is the provision of a corpectomy cage having telescoping members which are non-load bearing, and a load-bearing sleeve around the telescoping members.
A further objective of the present invention is the provision of a corpectomy cage having C-shaped telescoping members with aligned openings for receiving bone fusion material, and a sleeve to cover the openings so as to retain the fusion material within the cage.
Still another objective of the present invention is the provision of an improved corpectomy cage having minimal weight and increased strength.
A further objective of the present invention is the provision of an improved corpectomy cage which is economical to manufacture, and safe and durable in use.
These and other objectives will become apparent from the following description of the invention.